1. Field of the Invention
The present invention relates to a photoconductor for electrophotography and more particularly to a photoconductor having an undercoat layer for preventing the influence by the circumferential humidity and improving reliability thereof.
2. Description of the Prior Art
Up to the present, a low-price and pollution-free organic photosensitive material is used generally as a photoconductor for electrophotography (hereinafter to be referred to as a photoconductor) used in copying apparatuses of an electrophotographic system. Various photoconductors are known, for instance, a photoconductive resin type represented by polyvinylcarbazole (PVK), an electron-transfer complex type represented by PVK-TNF (2, 4, 7 trinitrofluorene), a pigment dispersion type represented by a phthalocyanine binder and a functionally distinguishable type using a charge generating substance in combination with a charge transporting substance. Among them, a functionally distinguishable photoconductor is specifically noticed.
When the Carlson process is used for image formation, these high sensitive photoconductors of functionally distinguishable organic types have the following problems:
(1) The photoconductor is hardly electrificated and its ability to retain an electric charge is poor, that is, the dark attenuation is high and the deterioration of characteristics is considerably high in repeated use.
(2) Non-uniformity of density and fog happen on the images obtained.
(3) Scumming happens in the case of the reversal development.
For the purpose of solving the above-mentioned problems, it is known that an intermediate layer is provided between a conductive substrate and a photosensitive layer as an undercoat layer of the photosensitive layer. The intermediate layers in which use are made of nylon type resins are disclosed in Japanese Patent Application Laying-open Nos. 47344/1973, 25638/1977, 30757/1983, 63945/1983, 95351/1983, 98739/1983 and 66258/1985. The intermediate layers in which use are made of maleic acid type resins are disclosed in Japanese Patent Application Laying-open Nos. 69332/1974 and 10138/1977. In addition, an intermediate layer in which use is made of polyvinylalcohol resin is disclosed in Japanese Patent Application Laying-open No. 105155/1983.
However, since an insulating resin is used as the undercoat layer in many cases, there were problems that the residual voltage of the photoconductor became high and the contrast of an image became poor. When a polyamide (Nylon(Trademark)) having a low electric resistance is used, it is possible to control the residual voltage. However, since a polyamide has a high water absorption, the characteristics of the photoconductor vary under the influence of a circumferencial humidity. For instance, in the reversal development system, fog occures under a high humidity circumstance and a density of the image decreases under a low humidity circumstance. In addition, there were also problems that the adhesion of a polyamide to an aluminum substrate with a rough surface is poor and it is impossible to cover the pinholes of the surface of the substrate.